Drum Brake System: Description and Operation

Leading/trailing drum brakes are used on vehicles with a 6450 pound GVW rating. Both brake shoes are held against the wheel cylinder pistons by the upper return spring and against the fixed anchor plate by the lower return spring. Applying the brakes causes the wheel cylinder pistons to move both shoes into contact with the drum. With forward wheel rotation, the forward brake shoe wraps into the drum and becomes self-energized. With reverse wheel rotation, the rear brake shoe is self-energized. Force from the brake shoes is transferred to the anchor plate through the backing plate and finally to the axle flange. Adjustment is automatic and occurs on any brake application. it is normal for the front (leading) shoe and lining assembly to wear faster than the rear (trailing) shoe and lining assembly.